Discussion on application of the Weibull distribution to electrical breakdown of insulating materials

The Weibull distribution is commonly used for statistical processing of breakdown data of electrical insulation. The statistical theory of breakdown that has been proposed since the 1970s has introduced a two-variables Weibull distribution in order to take into account both the stress applied and the failure times. In this paper this distribution is thoroughly discussed and then rejected. Indeed, the random variable is only one; the other is an independent variable that becomes random only through the first, with the same shape parameter. The case of breakdown after electrical or multiple-stress aging (electric strength test on aged specimens) is also examined and the probability distribution function is written even in the general case, where the probability is a function of several variables. Only one of the latter, i.e. the electric strength ES, is the random variable while the others, such as the applied stresses and the time at which the ES measurement is performed, are independent     

An experimental investigation of the electrical breakdown phenomena of interface insulation in prefabricated-type joints

To establish the reliability of the insulating performance of prefabricated-type joints (PJs), dielectric breakdown characteristics of interface insulation were studied. Using two types of electrodes, which simulate the interface configuration in an actual 275-kV PJ, ac and impulse BDSs, together with long-term performance of the interface, were evaluated under various conditions. Among the many factors which would influence the insulating characteristics of the interface, the effect of the silicone oil layer, as well as the applied external pressure, were examined. It was determined that the BDSs were influenced greatly by silicone oil application, by the applied interface pressure, and by the pretreatment of the surface of XLPE insulation. On the basis of the result of experiments, the functions of the silicone oil layer in the insulation interface of the PJ were examined. The authors concluded that the thinner silicone oil layer in the insulation interface is favorable for the establishment of the insulation interface of the PJ.     

New electric insulating materials for the insulation systems of rotating electrical machines

A wide range of nomenclature and properties for new materials for the insulation of high voltage electrical machines and traction motors of F and H insulation classes developed at Elinar Holding Company are presented in the report.     

Application of the Kalman filter for electrical endurancecharacterization of insulating materials and systems

The Kalman filter algorithm is applied to the results of accelerated life tests performed on insulating materials and systems carried out for electrical endurance characterization purposes. It consists of a recursive procedure that applies to the failure-time percentiles obtained from life tests, on the basis of the inverse power or the exponential models, and provides estimates of the endurance indices which give particular weight to the results of the life tests performed at the lowest test stresses. This allows more meaningful endurance characterization and accurate life prediction. This paper provides the algorithms for Kalman filter applications, giving emphasis to error estimation, as well as the method for calculation of confidence limits of life-line parameters and predicted failure times. The proposed Kalman filter procedure is applied to the experimental results of accelerated life tests relevant to different insulating materials and systems     

复合绝缘材料介电性能的相场模拟研究进展

相场方法在介观尺度范围内为复合材料的微观结构演化过程提供了一种有效的分析工具,填补了原子尺度微观模拟和宏观尺度模拟之间的跨度.本文首先综述了相场模型的理论基础,具体包括序参量选取原则、自由能泛函构建思路、相场动力学方程求解方法等.然后,介绍了相场模拟方法在复合绝缘材料本征构效关系、击穿演化机制、材料结构设计中的应用进展,并归纳出开展相场模拟有待深入研究的几个关键问题.分析指出,相场模拟可为复合绝缘材料的介电行为研究提供基础的方法论和半定量的解析手段,但目前仍缺乏涵盖不同建模尺度的统一仿真框架体系.     

复合绝缘子界面缺陷对电场分布特性影响的仿真研究

复合绝缘子的芯棒与护套粘接界面常常出现缺陷,畸变周围电场,影响绝缘子的电气和机械性能。为了研究不同缺陷形态下的绝缘子电场特性,文中以110 kV复合绝缘子为考察对象,应用有限元分析软件COMSOL搭建了绝缘子三维模型,对电场分布进行了仿真计算,研究了界面出现气隙、水汽等缺陷对局部电场及绝缘子整体轴向电场分布特性的影响。结果表明:气隙处电场强度相比正常情况下显著增大,场强最大值与气隙跨度、厚度正相关,与气隙长度负相关,并基于气隙等效弧柱体模型给出了理论分析,修正了等效圆柱模型的不足;水分渗入能降低气隙场强,但同时严重畸变绝缘子轴向电场;护套受潮增重会使场强线性增加,超过一定程度会引发电晕放电,导致沿面闪络等事故。     

Space charge formation and breakdown in polyethylene influenced by the interface with semiconducting electrodes

This paper deals with the influence of interface between polyethylene and semiconducting electrode on the space charge formation and electrical breakdown. Low‐density polyethylene (LDPE) films attached with different semiconducting electrodes were subjected to the DC breakdown test, and corresponding space charge distribution was measured. A heat treatment to LDPE itself did not bring about a significant change in space charge profile; however, when a semiconducting electrode was hot‐pressed, the impurities would migrate into LDPE at high temperature, leading to the change in space charge profile. Furthermore, it was suggested from the comparison between the results with degassed and as‐received semiconducting electrodes that some carriers relating to impurities in the electrode would move into LDPE under the voltage. In addition, it was shown that the breakdown is not determined by the field at the cathode which can supply sufficient electrons, but by the maximum field across the specimen, suggesting that an increase in conduction current due to the generation and/or injection, rather than the electronic avalanche process, leads to the breakdown. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 19–25, 2002     

Barrier effect of treeing in composite insulating materials with heat-adhesive interfaces of different polymers

A polymer/polymer composite system is widely used in high-voltage equipment and power cables. The interface of this composite system plays an important role in the electrical degradation, such as electrical treeing or partial discharge, of the composite system. Therefore, it is important to study the effect of an interface on the electrical treeing of polymer/polymer-composite insulating materials. In this paper, we describe the tree growth and complete breakdown characteristics of specimens with a polymer barrier film layer molded in ethylene vinyl acetate copolymer (EVA), in which the interface of EVA and the barrier film is perpendicular to the electric field under an AC voltage. It is found that with a barrier film, the tree growth is retarded on the barrier film, which then punctures the film, or develops along the edge of the film. It is also found that the pressure of decomposing gas in the tree channels plays an important role in tree propagation.     

On the dynamics of the electric field induced breakdown in lipidmembranes

Electric field methods are powerful tools for cell characterization and manipulation. Important biotechnological applications, e.g., electrofusion of cells or electroinjection of macromolecules into living cells, rely on membrane breakdown. Despite the widespread use of these techniques, the process of membrane breakdown is poorly understood: a better understanding can be expected to lead to higher efficiencies. The present study used planar lipid bilayers in order to limit the number of experimental parameters. Membrane rupture was induced by careful application of short electric field pulses: measurement of the subsequent increase in membrane conductivity with time permitted the underlying mechanism to be characterized. The initial process of pore formation starts a few μs after the onset of the pulse, and the ensuing breakdown of the entire lipid membrane occurs within about a millisecond (pore widening velocity of a few cm/s). The kinetics of the pore-opening process could be influenced qualitatively by adding surfactants and lipid-attached macromolecules, respectively. Changing the effective mass per unit area of membrane, which could be brought about by using known percentages of lipids with covalently bound, hydrophilic polymers, allowed a model for the pore widening process to be quantitatively tested     

Pressurizing and sub-cooling effects on electrical breakdown of LN2 in modeled HTS coils

Pressurizing and sub-cooling of liquid nitrogen are considered to have advantageous aspects in electrical insulation and the critical current in high temperature superconducting (HTS) coils. This paper deals with experimental studies on bubble behavior and partial breakdown (PBD) characteristics in a simulated electrode system of HTS coils immersed in pressurized liquid nitrogen, following our previous reports with saturated liquid nitrogen at atmospheric pressure. The tested electrode system consists of a coaxial coil layer to a cylindrical electrode with an insulation barrier and spacers. A heater is mounted inside the coil electrode to generate boiling which appears on quenched superconducting coils. Liquid nitrogen is pressurized to 0.2 MPa under constant temperature of ~77 K. The experimental results show that the partial discharge (PD) voltage is affected markedly by the bubble behavior which depends on the applied pressure to liquid nitrogen. Pressurization suppresses bubble growth in the insulation space and increases the inception voltage of PD. The charge quantity associated with a single PD at a given applied voltage increases with the applied pressure, and deterioration of solid insulation such as spacers and barriers is accelerated compared to that at atmospheric pressure if the PBD occurred     

电磁场对平行双线共模耦合特性研究

通过分析场线耦合所产生的差模电流与共模电流的差异,结合国内外的发展状况,研究了电磁场对平行双线的共模耦合模型;通过数值仿真,深入分析了共模电流随频率、位置等因素的变化规律;并进一步开展了实验研究,验证了数值结果的可靠性。本文的研究成果可为电磁兼容性工程设计提供参考。     

An experimental study of the flux control characteristics of a magnetic fluid controlled by a parallel or orthogonal magnetic field

This paper presents experimental results of the flux control characteristic and the inductance control characteristic of magnetic fluid which is controlled by the permanent magnets. Two kinds of magnetic field, parallel and orthogonal, are discussed comparatively. The position between the magnetic fluid and the permanent magnet determines the magnetic field. The results are useful when employing magnetic fluid as a sensor or a control element.     

Benefits and challenges of using unmanned aerial systems in the monitoring of electrical distribution systems

This paper presents a study coming from an academic and industry partnership with the goals of exploring potential uses for UAS in distribution system operation and maintenance, establishing baseline costs and capabilities via equipment field tests, and simulating the cost benefits of increased maintenance. Existing UAS technology is shown to be capable of providing situational awareness for disaster response as well as increasing the number of maintenance inspections and speeding them up.     

A new composite index of reliability of supply in the industrial systems with distributed generation

Distributed generators (DGs) integrated into distribution networks could affect the host network in number of ways. In this paper an assessment of the impact of the DG continuously operated, which output behavior is non-stochastic, on the reliability of supply in the industrial networks, is performed. A set of new indices representing impact of DG on the interruption frequency, interruption duration and expected energy not supplied to every single customer, is introduced. In addition, a new composite index compiling the impacts of DG on the overall reliability of supply, including interruption frequency, interruption duration and expected energy not supplied, is proposed. Results obtained from several case studies using real-life industrial network are presented and discussed.     

并行采集系统触发晃动实时校正技术研究

在并行实时采集系统,大量的采用了并行时间交替采样和数据分相存储技术,但采样数据的并行存储将引起触发抖动问题,严重降低了整个系统的性能。在分析触发抖动原因的基础上,提出了采用时间内插计数法,通过实时放大并测量触发信号和并行采样时钟的时间间隔,对触发晃动进行校正,从而达到降低触发抖动,提高波形显示稳定性的目的,并结合工程应用,在采用8路拼合的2GSPS实时采样数字存储示波器中实现了对触发晃动的校正,最后给出了该功能的性能测试结果。     

PD inference for the early detection of electrical treeing in insulation systems

Partial discharge (PD) measurements constitute one of the most promising tools for electrical insulation diagnosis. This paper describes how a procedure based on PD measurements can provide early detection of electrical trees in polymeric insulation systems. Such an application relies upon a new methodology, which provides enhanced tools for the identification of PD generating defects. Tree inference is carried out stepwise. Acquired signals are primarily separated according to their waveform, thus achieving data sets related to a specific PD typology. Then, fuzzy algorithms are applied to PD height and phase derived quantities belonging to these homogeneous data sets, in order to assign a membership degree to specific output categories. If the data set is relevant to an internal defect, a further analysis is performed in order to establish whether or not this defect is a treed region. The algorithm described in this paper was developed resorting to tests performed on artificial test specimens and electrical apparatus. In particular, the rules to detect the presence of electrical trees were derived from experiments carried out on needle-plane objects, constituted by slabs of cross-linked polyethylene (XLPE) where a needle is inserted and partially extracted in order to generate a cavity in front of the needle tip. Tests were also performed on cables having artificial defects., as well as on other insulation systems, such as high frequency transformers. Applications of the proposed approach to MV cables and to HV transformers show that electrical trees can be detected successfully before final breakdown.     

大气电场仪观测资料数字序列的时间特征分析

根据某大气电场仪的数据传输方式,按照数据包接收端的计算机时间和数据包顺序号,利用最小二乘法对观测数据做分段直线拟合、建立分段线性关系,求得数据包平均时间间隔和数据包参考时间,进而在无线通讯网络堵塞情况下对被延时的数据包进行到达时间的修正、计算出每个场强值的观测时间,从而达到提高数据序列的可读性、提高宝贵的实测资料的利用价值之目的。此方法成功地恢复了该类型大气电场仪组网观测所获得的一批观测资料的观测时间,为这些资料的专业分析和应用提供了保障。     

On the use of electrical precompensation of dispersion in optical single-sideband transmission systems

The use of electrical predistortion in optical single-sideband (OSSB) transmission systems is proposed to extend the tolerance to fiber dispersion impairment. Due to the spectral properties of OSSB signals, a simple electrical dispersive line can be used to mitigate the fiber dispersion, reducing the complexity of electrical predistortion methods proposed recently for optical modulations other than OSSB. Carrier-suppressed and carrier-unsuppressed optical modulations can be compensated by such technique, extending the range compared to previously reported works on fiber dispersion mitigation after direct detection using OSSB signals, where only carrier-unsuppressed modulations can be effectively compensated. The use of electrical precompensation is investigated for three signaling formats: Nonreturn to zero, return to zero, and alternate mark inversion (AMI). Due to distortion occurring in the sideband suppression process, signaling formats with reduced duty cycles present improved performance as a consequence of enhanced tolerance to intersymbol interference. Using such formats with electrical predistortion, the reach limitation arises not from fiber dispersion but from nonlinear impairments and optical noise accumulation. Using AMI and ideal electrical predistortion, distances greater than 1200 km of standard single mode fiber are achieved at 10 Gb/s with bit error ratio (BER) lower than 10/sup -12/, without using optical dispersion compensation. Introducing accurate models for the electrical dispersive lines, the transmission distance is reduced to 720 km for BER lower than 10/sup -12/.     

电网中性点经消弧线圈并电阻接地方式的研究

电网中性点采用经消弧线圈并电阻接地,可借电阻接地之长弥补消弧线圈接地之短,有效地抑制电弧接地过电压,使正常运行时的中性点位移电压不致过大.在这种接地方式下,利用计算机对消弧线圈进行控制,使其根据电网总电容电流的大小自动跟踪补偿,始终使接地电流最小,保证煤矿生产安全、顺利地进行.